Digital cameras, scanners, and other imaging devices often use image sensors, such as charge-coupled device (CCD) image sensors or complementary metal-oxide-semiconductor (CMOS) image sensors, to convert optical signals to electrical signals. An image sensor typically includes a grid of pixels, row access circuitry, column access circuitry, and a ramp signal generator. The pixels capture the light impinged on them and convert the light signals to electrical signals. The row access circuitry controls which row of pixels that the sensor will read. The column access circuitry includes column read circuits that read the signals from corresponding columns. The ramp signal generator generates a ramping signal as a global reference signal for column read circuits to record the converted electrical signal. In operation, the quality of the ramping signal can significantly affect the quality of the output of the image sensor. For example, a ramping signal with poor linearity can cause a gain non-linearity of the column read circuits. In addition, a ramping signal with a large glitch power can have a lost-bit effect. Moreover, a ramp signal generator with low power consumption and a small physical area is often desired.